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Sean J. McCafferty, MD, FACS
Nathan M. Radcliffe, MD, ABO
Evaluate corneal rigidity changes following corneal crosslinking (CCL) by paired differential tonometry IOP measurements with a Goldmann tonometer (GAT) using both a standard GAT prism and corneal compensating GAT prism.
IOP was measured on 18 unique eyes undergoing CCL for keratoconus with a GAT using a standard flat prism and a curved corneal error correcting prism before treatment and 2 weeks, 2 months and 6 months after treatment. Concurrent measurements of Central corneal thickness CCT and corneal hysteresis CH were completed.
Paired IOP measurements with standard and corneal correcting GAT prisms indicated a significant sustained relative increase in the differential IOP between the two prisms after CCL (p=0.005,0.015). CH initially decreased at two weeks post-CCL then returned to sustained pre-op levels (p=0.033,0.20). CCT progressively decreased following CCL (p=0.002).
Differential tonometry between standard and corneal biomechanical compensating GAT prisms demonstrated it as a simple and sensitive measurement of changes in corneal rigidity and corneal stress redistribution.
Elias F. Jarade, MD
Inducing fibrogenesis and new interfibrillary bonds in post-LASIK ectasia was previously reported as new treatment for ectasia aiming for the reintegration of the created LASIK flap into the residual corneal stroma in ectatic corneas. The aim of this study is to evaluate the long term safety and efficacy of this technique (up to 1 year follow up)
This is a prospective study of patients who were treated with fibrogenesis for iatrogenic corneal ectasia after LASIK surgery. The Fibrogenesis technique is described elsewhere by Jarae et al. Patients were closely followed up up to 1 year. Slit lamp exam, Uncorrected distance visual acuity (UCDVA), Corrected distance visual acuity (CDVA), manifest refraction and corneal tomography maps were recorded at baseline, 6 months and 1 year post treatment. The Keratometry readings and corneal thickness were obtained using Pentacam Scheimpflug imaging the WaveLight® Allegro Oculyzer™ (WaveLight, GmbH, Erlangen, Germany). results, complications and patient's satisfactions were all recorded
22 eyes with post-LASIK ectasia who underwent the procedure were included. At 6 months there was a statistically significant reduction in SE by 1.26 ±1.79 D; p= 0.003, and a small increase in mean central corneal thickness (CCT) by 8.68 ± 19.43; p= 0.048. K-mean remained stable. At 1 year,there is reduction in SE from baseline by 1.08 ± 2.15 D; p=0.032 and there was also a statistically significant decrease of K-mean by 1.34 ± 1.96 D; p=0.004. However, the improvement in mean CCT was no longer present. CDVA, cylinders and K max remained stable. UCDVA has had a trend to improve without reaching a statistically significant level. No complications were noted up to one year Follow up
Up to one year follow-up, Inducing fibrogenesis and new interfibrillary bonds is considered as safe and effective new treatment for post LASIK ectasia. Primary data suggests an improvement from baseline in spherical error and K-mean. Those findings need to be consolidated, in the future, by a larger sample size and a longer follow up period
Hormoz Abdshahzadeh Sr., MD
Farhad Hafezi, MD, PhD
J. Bradley Randleman, MD
Francesca Gilardoni, MD
Emilio A. Torres Netto, MD
Reyhaneh Abrishamchi, MD
Oxygen diffusion has a central role in the efficiency of corneal cross-linking. Oxygen availability in tissue increases with reduced temperature. The goal of this study was to assess whether a reduction of the corneal temperature during CXL might raise oxygen availability and thus enhance the biomechanical effect of CXL in ex vivo porcine corneas.
One hundred twelve porcine corneas with intact epithelium were divided into 4 groups and analyzed. Prior to corneal soaking with hypo-osmolaric 0.1% riboflavin, the epithelium was removed manually in all groups. Accelerated epithelium-off CXL using 9 mW/cm2 irradiance for 10 minutes was performed either at room temperature (group 1, 24°C) or in a cold room (group3, 4°C). Non-cross-linked corneas (groups 2 and 4) were subjected to the same temperatures and served as controls. The elastic modulus of 5-mm wide corneal strips was analyzed and used to determine corneal biomechanical properties.
Epithelium-off CXL led to significant increases in the elastic modulus determined between 1% and 5% of strain in stress-strain extensometry when compared to non-cross-linked controls, both at 24°C (p<0.001) and 4°C (p=0.006) . However, no significant difference was found between corneas treated with CXL at 24°C and 4°C (p = 0.384).
While oxygen plays a central role in corneal cross-linking, the potentially increased diffusion of oxygen in lower tissue temperatures does not appear to play a significant role in the biomechanical efficiency of epithelium-off CXL accelerated protocols in ex vivo porcine corneas.
J. Bradley Randleman, MD
After epithelium debridement, LASIK flaps were created on all intact fresh porcine eyes with a mechanical microkeratome. Then, CXL over the flap (S-CXL) or CXL under the flap (Flap-CXL) was performed. For S-CXL, riboflavin was dropped on the corneal surface followed by 3 mW/cm2 UV exposure with the flap in place for 30 minutes. For Flap-CXL, riboflavin was dropped on the stromal bed after reflecting the flap followed by the same UVA exposure with the flap replaced. Depth profile of stiffness variation and averaged elastic modulus of anterior, middle and posterior stroma were determined by analyzing Brillouin maps.
S-CXL had maximal stiffening impact at the corneal surface with a Brillouin shift of 8.40±0.04 GHz, while Flap-CXL had maximal stiffening impact 249±34 μm under the corneal surface (including 116±10 μm flap) with a Brillouin shift of 8.22±0.03 GHz (p<0.001). S-CXL increased longitudinal modulus by 6.69% in the anterior, 0.48% in the middle, and -0.91% in the posterior regions as compared to Flap-CXL which increased longitudinal modulus by 3.43% in the anterior (p<0.001), 1.23% in the middle (p<0.1), and -0.78% in the posterior regions (p=0.68).
The standard CXL technique for treatment after LASIK flap creation generates significantly greater stiffening effect in the anterior cornea than using a modified protocol with riboflavin administration under the flap. Minimal middle or posterior corneal stiffening occurs with either protocol.
Renato Ambrósio, MD, PhD
Louise Esporcatte, MD
Marcella Salomão, MD
Guilherme Hilgert, MD
Nelson Sena Jr., MD
To compare the ability of tomographical parameters, biomechanical parameters and the integration of both approaches for discriminating ectatic disease.
A retrospective study involving a total of 1295 eyes divided into 736 normal eyes (group 1), 321 KC eyes (group 2), 113 unoperated ectatic eyes from patients with very asymmetric ectasia (group 3), who presented fellow eyes (125 eyes) with normal topographic maps (group 4). For groups 1 and 2, only one eye per patient was selected randomly for the inclusion in the study, in order to avoid the bias of the relation between eyes. Tomographic parameters included ISV, BADD, PRFI and TKC. Biomechanical parameters included SPA1, Inverse radius, DA Ratio, and CBI. The TBI was also evaluated.
With a cut-off value of 0.79, TBI had 100% sensitivity and specificity to detect frank ectasia cases (AUC = 1.0 in groups 2 and 3); however, for the correct characterization of eyes with standard topography having no definitive signs of ectasia from patients with clinical ectatic disease in the fellow eye, an optimization of cut-off value was necessary, and a value of 0.29 provided 90.4% sensitivity with 4% false-positive results (96% specificity; AUC = 0.985). Comparing all groups, the AUC of the TBI to detect ectasia (groups 2, 3 and 4) was 0.992 and had a statistically higher AUC (DeLong, p<0.001) than all other parameters tested for every analysis performed.
The integration of biomechanical data and corneal tomography with artificial intelligence data augments the sensitivity and specificity for screening and enhancing early diagnosis of patients with corneal ectasia. The AUC of the TBI was statistically higher than all other analyzed parameters, including the CBI.